Lack of physical activity has been identified as the third highest risk behavior for the development of a host of diseases. Tentative evidence from both human and animal models suggests that there may be a genetic factor that controls the amount of physical activity that is accomplished by an individual. Therefore, our broad, long-term objective is to identify the genes and/or genetic factors responsible for the control of physical activity level. The proposed project will be the first step toward the fulfillment of this long-term objective and has as its goal to identify progenitor strains and complete a segregation analysis, which can be used in future, advanced genetic studies. Within this project, we aim to determine: (Specific Aim 1) The range of biological responsiveness in physical activity level by assessing interstrain variation in inbred mice; and (Specific Aim 2) The pattern of genetic control of physical activity level by examining progeny from inbred progenitor strains that exhibit high physical activity levels (HIGH) and low physical activity levels (LOW) phenotypes to voluntary wheel-running exercise. The Specific Aims, when fulfilled, will be significant given the health risk of diseases either directly caused by or exacerbated by lack of physical activity. Understanding the factors that predispose an individual to a certain physical activity level could lead to better methods of improving the physical health and well-being of individuals. Unlike other past attempts, this project is unique in that we are proposing to use common, but powerful, genetic research techniques to investigate this area. This will be the first project investigating the genetic basis of physical activity level to use these techniques that have already proven successful in other fields (e.g. cystic fibrosis).